Electron Beam Heating Research Articles

Numerical Simulation of Temperature Field in Steel under Action of Electron Beam Heating Source

It is impossible to improve the most critical performance properties of machine parts without methods of modifying the surface layer using such concentrated energy as laser, plasma, an electron beam or high-frequency currents. For the rational use of these methods, which are characterized by high heating rates, i.e. about 104 ... 105oC/sec a reliable mechanism for determining the processing modes that ensure the required level of quality characteristics of the hardened surface layer of machine parts, is essential. In this paper, the interrelation between the parameter values of thermal cycles, implemented in the surface layer of steel U8, and the modes of electron beam heating in the atmosphere has been determined.

Electromagnetic properties of Li0.4Fe2.4Zn0.2O4 ferrite sintered by continuous electron beam heating

Lithium-zinc ferrite with the chemical formula of Li0.4Fe2.4Zn0.2O4 was prepared by continuous electron beam heating with electron energy of 1.4MeV at 1100°C for 140min. X-ray diffraction analysis confirmed the formation of cubic spinel structure. From SEM analysis, the average grain size of the ferrite ceramic was 2µm. The electromagnetic properties of LiZn ferrite were investigated. The samples are characterized by high values of the saturation magnetization, initial permeability and Curie temperature. The value of electrical resistivity is equal to 2.3×103Ωcm. The high frequency performance of LiZn ferrite samples was estimated by measurement the frequency dispersion of the dielectric constant and dielectric loss. It was shown that the dielectric constant is characterized by normal dielectric behavior with frequency. The results were compared with the previous results obtained for the samples prepared by pulsed electron beam heating.

Nanoscale Schottky barrier mapping of thermally evaporated and sputter deposited W/Si(001) diodes using ballistic electron emission microscopy

Ballistic electron emission microscopy has been utilized to demonstrate differences in the interface electrostatics of tungsten-Si(001) Schottky diodes fabricated using two different deposition techniques: thermal evaporation using electron-beam heating and magnetron sputtering. A difference of 70 meV in the Schottky barrier heights is measured between the two techniques for both p- and n-type silicon even though the sum of n- and p-type Schottky barrier heights agrees with the band gap of silicon. Spatially resolved nanoscale maps of the Schottky barrier heights are uniform for the sputter film and are highly disordered for the e-beam film. Histograms of the barrier heights show a symmetric Gaussian like profile for the sputter film and a skewed lognormal distribution for e-beam film. A Monte-Carlo model is developed to simulate these histograms which give strong indication that localized elastic scattering is causing this skewing as forces the hot electrons to need a greater total energy to surmount the barrier. These differences are attributed to silicide formation from the unintentional substrate heating during the e-beam deposition, which is confirmed with transmission electron microscopy.

Coating synthesis controlled by electron-beam heating

The methods of combined electron-beam treatment of parts made of steel with one- and two-layer coatings are studied experimentally. Ti-Ni, Ni-Al and Al-Ti systems were used as the examples in the experiments. The mathematical model is suggested for coating formation in the controlled regime of high temperature synthesis during high energy source motion along the preliminarily deposited layer of exothermic composition. The study takes into account the difference in thermophysical properties of the materials of coating and substrate, heat release from chemical reaction that leads to the coating properties formation and other factors. The realization of the synthesis depends on technological parameters. Various regimes of the treatment process are investigated numerically.

Plasma diagnosis as a tool for the determination of the parameters of electron beam evaporation and sources of ionization

The atomic vapor generated by electron beam heating is partially ionized due to atom–atom collisions (Saha ionization) and electron impact ionization, which depend upon the source temperature and area of evaporation as compared to the area of electron beam bombardment on the target. When electron beam evaporation is carried out by inserting the target inside an insulating liner to reduce conductive heat loss, it is expected that the area of evaporation becomes significantly more than the area of electron beam bombardment on the target, resulting in reduced electron impact ionization. To assess this effect and to quantify the parameters of evaporation, such as temperature and area of evaporation, we have carried out experiments using zirconium, tin and aluminum as a target. By measuring the ion content using a Langmuir probe, in addition to measuring the atomic vapor flux at a specific height, and by combining the experimental data with theoretical expressions, we have established a method for simultaneously inferring the source temperature, evaporation area and ion fraction. This assumes significance because the temperature cannot be reliably measured by an optical pyrometer due to the wavelength dependent source emissivity and reflectivity of thin film mirrors. In addition, it also cannot be inferred from only the atomic flux data at a certain height as the area of evaporation is unknown (it can be much more than the area of electron bombardment, especially when the target is placed in a liner). Finally, the reason for the lower observed electron temperatures of the plasma for all the three cases is found to be the energy loss due to electron impact excitation of the atomic vapor during its expansion from the source.

A three-dimensional transient thermal-fluid flow-compositional study of ingot casting during electron beam remelting of Ti–6Al–4V

Electron beam cold hearth remelting (EBCHR) is a consolidation and refining process capable of consolidating titanium scrap and sponge material into high quality titanium alloy ingots. During the final stage of casting in the EBCHR process, operators must balance the potential to form large shrinkage voids, caused by turning off the electron beam heating, against the tendency to evaporate alloying additions, which occurs if the top surface remains molten. A comprehensive understanding of the evaporation and fluid flow conditions occurring during the final stage of EBCHR is required in order to optimize ingot production. This research focused on developing a coupled thermal, fluid flow and composition model, capable of predicting the temperature, fluid flow and composition fields within an EBCHR cast, Ti–6Al–4V ingot. The physical phenomena of thermal and compositional buoyancy, mushy zone flow attenuation and aluminum evaporation were incorporated in the model formulation. Industrial scale experiments were carried out at the production facilities of a leading industrial producer of titanium to provide data and measurements for model verification. Model predictions for liquid pool profile, last liquid to solidify and composition fields are in good agreement with the industrially measured results. A sensitivity analysis was performed with the model to study the effects of variation of electron beam power input and hot top time duration on the evaporative losses and position of solidification voids. For the cases examined, there was a strong correlation between electron beam power and alloying element losses, while hot top duration variation results indicated a stronger dependence on last liquid to solidify than on alloying element losses. Therefore a classic optimization problem arises between balancing hot top duration with alloying element losses.

Electron-irradiation-induced crystallization at metallic amorphous/silicon oxide interfaces caused by electronic excitation

Irradiation-induced crystallization of an amorphous phase was stimulated at a Pd-Si amorphous/silicon oxide (a(Pd-Si)/SiOx) interface at 298 K by electron irradiation at acceleration voltages ranging between 25 kV and 200 kV. Under irradiation, a Pd-Si amorphous phase was initially formed at the crystalline face-centered cubic palladium/silicon oxide (Pd/SiOx) interface, followed by the formation of a Pd2Si intermetallic compound through irradiation-induced crystallization. The irradiation-induced crystallization can be considered to be stimulated not by defect introduction through the electron knock-on effects and electron-beam heating, but by the electronic excitation mechanism. The observed irradiation-induced structural change at the a(Pd-Si)/SiOx and Pd/SiOx interfaces indicates multiple structural modifications at the metal/silicon oxide interfaces through electronic excitation induced by the electron-beam processes.

Potential application of carbon nanotube core as nanocontainer and nanoreactor for the encapsulated nanomaterial

Fe3C nanorod filled inside carbon nanotube has been irradiated inside transmission electron microscope at both room and high temperature. In-situ response of Fe3C nanorod as well as CNT walls has been studied. It has been found that when electron irradiation is performed at room temperature (RT), nanorod first bends and then tip makes at the end whereas at high temperature (∼490°C) nanorod slides along the tube axis and then transforms into a faceting particle. Extrusion of solid particle filled in the core of CNT has also been demonstrated. It is suggested that these morphological changes in nanorod may have happened due to the compression which was generated either by shrinkage of tube or by local electron beam heating. Presented results demonstrate that CNT core could be used as nano-container or reactor.

Magnetization study in solid state formation of lithium-titanium ferrites synthesized by electron beam heating

The solid state formation of substituted lithium-titanium ferrites with chemical formula Li0.5(1+х)Fe2.5−1.5xTixO4 (х = 0.2; 0.4) prepared by two different methods were studied by X-ray diffraction and saturation magnetization analyzes. For the first method, lithium-titanium ferrites were prepared by conventional solid state synthesis in laboratory furnace at temperatures of 600, 700 and 750 °C and times of 0, 10, 20, 30, 60, and 120 min. For the second method, the samples were obtained by heating of reaction mixtures in high-energy (2.4 MeV) electron beam using similar time-temperature mode. XRD analysis results for all samples showed a high degree formation of lithium-titanium ferrites, obtained by high-energy electron beam heating at lower temperatures and times of synthesis compared with standard thermal heating. Such samples are characterized by the high values of saturation magnetization due to lithium-titanium ferrites formation. The observed radiation effect consists in significant decrease of the temperature and time of ferrite synthesis compared to conventional thermal heating in high-temperature furnaces.

Study of the pores inside tungsten coating after thermal cycling for fusion device

In the next fusion devices, all the plasma facing components will consist of bulk tungsten or tungsten coating on carbon. This paper focuses on the behaviour of tungsten coated on carbon fibre composite designed for the WEST project (Bucalossi et al 2011 Fusion Eng. Des. 86 684–688) under intensive thermal cycling delivered by an electron beam. The use of scanning electron microscope has allowed in particular, the observation of several pore lines inside the coating. These pore lines have different aspects depending on the observed zone according to the localisation of the electron beam, accentuated lines with more numerous enlarged pores in zone exposed to the electron beam. An analogous trend is also observed for JET tungsten-coated samples under similar thermal cycles despite their different properties due to an alternative manufacturing method of the substrate. A systematic and attentive comparison on the coating changes after the application of the electron beam heating is presented. The observed comportments as the formation of the pore lines or the pore shapes are assumed to be inherent to simultaneous diffusion processes. In association with the pore line formation, a migration of the carbon substrate towards the surface is presumed and discussed.

SIMULTANEOUS IRIS AND HINODE/EIS OBSERVATIONS AND MODELING OF THE 2014 OCTOBER 27 X2.0 CLASS FLARE

ABSTRACT We present a study of the X2-class flare which occurred on 2014 October 27 and was observed with the Interface Region Imaging Spectrograph (IRIS) and the EUV Imaging Spectrometer (EIS) on board the Hinode satellite. Thanks to the high cadence and spatial resolution of the IRIS and EIS instruments, we are able to compare simultaneous observations of the Fe xxi 1354.08 Å and Fe xxiii 263.77 Å high-temperature emission (≳10 MK) in the flare ribbon during the chromospheric evaporation phase. We find that IRIS observes completely blueshifted Fe xxi line profiles, up to 200 km s−1 during the rise phase of the flare, indicating that the site of the plasma upflows is resolved by IRIS. In contrast, the Fe xxiii line is often asymmetric, which we interpret as being due to the lower spatial resolution of EIS. Temperature estimates from SDO/AIA and Hinode/XRT show that hot emission (log(T[K]) > 7.2) is first concentrated at the footpoints before filling the loops. Density-sensitive lines from IRIS and EIS give estimates of electron number density of ≳1012 cm−3 in the transition region lines and 1010 cm−3 in the coronal lines during the impulsive phase. In order to compare the observational results against theoretical predictions, we have run a simulation of a flare loop undergoing heating using the HYDRAD 1D hydro code. We find that the simulated plasma parameters are close to the observed values that are obtained with IRIS, Hinode, and AIA. These results support an electron beam heating model rather than a purely thermal conduction model as the driving mechanism for this flare.

Fabrication of Tungsten & Tungsten Alloy and its High Heat Load Testing for Fusion Applications

Pure Tungsten (W) & Tungsten-lanthanum oxide (WL) were fabricated using Direct Sintering Press. W & WL found to be very good thermo-mechanical properties with higher densification desired for Plasma Facing Material. Both materials were subjected to transient high heat load conditions relevant to the ITER-like Divertor to study the material behavior using high heat flux test facility with electron beam heat source. Surface heat load of 1.0–3.14 MJ/m2 energy density applied on W & WL with pulse duration of 20 ms. The crack formations and surface modification behaviors of material under high heat load were investigated with detailed characterization.

Linear and Nonlinear Electron Beam Heating of Magnetized, Motional, and Dusty Plasma

Recent theoretical work on electron beam heating of magneto-active motional Plasma is presented. Power transfer from beam (plasma heating) and generated electric fields for different physical situations of linear and nonlinear beam-plasma interaction, are studied. Based on previous works [1] [2], we shall study the effects of dusts and plasma motion () on plasma heating. Besides, the case of an inhomogeneity of beam velocity () is also considered. Taking into consideration nonlinear process, dust, plasma motion, and beam velocity inhomogeneity, are found to play a crucial role via power absorbed by the beam and the generated electric field in the system.

Electron Irradiation Effects of SrZrO3 Ceramic for Radioactive Strontium Immobilization

The perovskite structure is widely considered ideal host phases for Sr immobilization. To investigate the radiation tolerance on ceramic waste forms, the as-prepared SrZrO3 ceramics were irradiated by external electron beam. The results indicated that the electron irradiation had different influence on the surface and inside of the SrZrO3 ceramic. The no-crystallizing can be produced on the surface of SrZrO3 ceramic, and electron beam heating promoted grain growth in the inside of SrZrO3.

Electron irradiation induced buckling, morphological transformation, and inverse Ostwald ripening in nanorod filled inside carbon nanotube

The present study aims to deduce the in-situ response of iron carbide (Fe3C) nanorod filled inside carbon nanotube (CNT) under electron irradiation. Electron irradiation on Fe3C filled-CNT at both high and room temperature (RT) has been performed inside transmission electron microscope. At high temperature (HT), it has been found that γ-Fe atoms in lattice of Fe3C nanorod accumulate first and then form the cluster. These clusters follow the inverse Ostwald ripening whereas if e-irradiation is performed at RT then only the morphological changes in both carbon nanotube as well as nanorod are observed. Compression generated either by electron beam heating or by shrinkage of CNT walls is observed to be a decisive factor.

Mechanisms of Electron-Beam-Induced Damage in Perovskite Thin Films Revealed by Cathodoluminescence Spectroscopy

Electron-beam-induced damages in methylammonium lead triiodide (MAPbI3) perovskite thin films were studied by cathodoluminescence (CL) spectroscopy. We find that high-energy electron beams can significantly alter perovskite properties through two distinct mechanisms: (1) defect formation caused by irradiation damage and (2) phase transformation induced by electron-beam heating. The former mechanism causes quenching and broadening of the excitonic peaks in CL spectra, whereas the latter results in new peaks with higher emission photon energy. The electron-beam damage strongly depends on the electron-beam irradiation conditions. Although CL is a powerful technique for investigating the electronic properties of perovskite materials, irradiation conditions should be carefully controlled to avoid any significant beam damage. In general, reducing acceleration voltage and probing current, coupled with low-temperature cooling, is more favorable for CL characterization and potentially for other scanning electron-b...

HOW IMPORTANT ARE ELECTRON BEAMS IN DRIVING CHROMOSPHERIC EVAPORATION IN THE 2014 MARCH 29 FLARE?

We present high spatial resolution observations of chromospheric evaporation in the flare SOL2014-03-29T17:48. Interface Region Imaging Spectrograph (IRIS) observations of the FeXXI 1354.1 A line indicate evaporating plasma at a temperature of 10 MK along the flare ribbon during the flare peak and several minutes into the decay phase with upflow velocities between 30 km s$^{-1}$ and 200 km s$^{-1}$. Hard X-ray (HXR) footpoints were observed by RHESSI for two minutes during the peak of the flare. Their locations coincided with the locations of the upflows in parts of the southern flare ribbon but the HXR footpoint source preceded the observation of upflows in FeXXI by 30-75 seconds. However, in other parts of the southern ribbon and in the northern ribbon the observed upflows were not coincident with a HXR source in time nor space, most prominently during the decay phase. In this case evaporation is likely caused by energy input via a conductive flux that is established between the hot (25 MK) coronal source, which is present during the whole observed time-interval, and the chromosphere. The presented observations suggest that conduction may drive evaporation not only during the decay phase but also during the flare peak. Electron beam heating may only play a role in driving evaporation during the initial phases of the flare.

Electron beam induced etching of carbon

Nanopatterning of graphene and diamond by low energy (≤30 keV) electrons has previously been attributed to mechanisms that include atomic displacements caused by knock-on, electron beam heating, sputtering by ionized gas molecules, and chemical etching driven by a number of gases that include N2. Here, we show that a number of these mechanisms are insignificant, and the nanopatterning process can instead be explained by etching caused by electron induced dissociation of residual H2O molecules. Our results have significant practical implications for gas-mediated electron beam nanopatterning techniques and help elucidate the underlying mechanisms.

Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

We investigated the response of the solar atmosphere to non-thermal electron beam heating using the radiative transfer and hydrodynamics modelling code RADYN. The temporal evolution of the parameters that describe the non-thermal electron energy distribution were derived from hard X-ray observations of a particular flare, and we compared the modelled and observed parameters. The evolution of the non-thermal electron beam parameters during the X1.5 solar flare on 2011 March 9 were obtained from analysis of RHESSI X-ray spectra. The RADYN flare model was allowed to evolve for 110 seconds, after which the electron beam heating was ended, and was then allowed to continue evolving for a further 300s. The modelled flare parameters were compared to the observed parameters determined from extreme-ultraviolet spectroscopy. The model produced a hotter and denser flare loop than that observed and also cooled more rapidly, suggesting that additional energy input in the decay phase of the flare is required. In the explosive evaporation phase a region of high-density cool material propagated upward through the corona. This material underwent a rapid increase in temperature as it was unable to radiate away all of the energy deposited across it by the non-thermal electron beam and via thermal conduction. A narrow and high-density ($n_{e} \le 10^{15}$ cm$^{-3}$) region at the base of the flare transition region was the source of optical line emission in the model atmosphere. The collision-stopping depth of electrons was calculated throughout the evolution of the flare, and it was found that the compression of the lower atmosphere may permit electrons to penetrate farther into a flaring atmosphere compared to a quiet Sun atmosphere.

Site specific control of crystallographic grain orientation through electron beam additive manufacturing

Site specific control of the crystallographic orientation of grains within metal components has been unachievable before the advent of metals additive manufacturing (AM) technologies. To demonstrate the capability, the growth of highly misoriented micron scale grains outlining the letters D, O and E, through the thickness of a 25·4 mm tall bulk block comprised of primarily columnar [001] oriented grains made of the nickel base superalloy Inconel 718 was promoted. To accomplish this, electron beam scan strategies were developed based on principles of columnar to equiaxed transitions during solidification. Through changes in scan strategy, the electron beam heat source can rapidly change between point and line heat source modes to promote steady state and/or transient thermal gradients and liquid/solid interface velocity. With this approach, an equiaxed solidification in the regions bounding the letters D, O and E was achieved. The through thickness existence of the equiaxed grain structure outlining the letters within a highly columnar [001] oriented bulk was confirmed through characterizing the bulk specimen with energy selective neutron radiography and confirming with an electron backscatter detection. Ultimately, this demonstration promotes the ability to build metal components with site specific control on crystallographic orientation of grains using the electron beam melting process.